Testing device with a drive, which converts to a rotational movement into a reciprocating movement of variable amplitude

ABSTRACT

The invention relates to a testing device for the static and dynamic testing of workpieces, comprising a first clamping device and a second clamping device for the workpiece, and a drive for the cyclical displacement of the second clamping device, wherein the drive has a rocker arm on which the second clamping device is pivotably mounted and the two ends of the rocker arm are connected in each case to a pivotably mounted link, and the free ends of the links are coupled in each case to a crank drive, wherein the links protrude from the ends of the rocker arm in the same direction in the basic position of the testing device.

The invention relates to a test device for the static and dynamictesting of workpieces, having a first, fixed clamping device and asecond, movable clamping device for the workpiece, and a drive formoving the second clamping device, where the drive has a rocker on whichthe second clamping device is mounted in a rotatable manner, and the twoends of the rocker are each connected to a rotatably mounted connectingrod, and the free ends of the connecting rods are each coupled to acrank mechanism.

The test machine is based on the principle of the generation of a strokeby means of a crank mechanism. Since the stroke has to be controlledcontinuously during operation for some component tests and thereforemust be adjustable, a simple means of adjustment during runningoperation, which in addition is as far as possible free from wear, isnecessary.

A means of adjusting the amplitude during operation is known fromGB450,347. In this device, a rocker is driven by two cams. Adjustment ofthe phase position of the cams with respect to one another gives rise todifferent strokes, from 0 to twice the throw of the cams. A disadvantagein this arrangement is the necessity for slide blocks. These have tosupport the counterpressure, and are at the same time subject to asignificant relative movement during each stroke, meaning that high wearcan be expected.

This problem of the basic principle was recognized, for example, inFR1388925 and overcome by making the connection to the rocker by meansof two connecting rods. However, this mechanism has the disadvantagethat it is not possible to produce strokes which are as small as desiredtherewith. This is necessary on the one hand for “starting” a testmachine, since otherwise it may not be possible to apply the requireddrive energy of the drive in order to subject the sample to the desiredload, and on the other hand the smallest possible stroke may already beso large that it overloads the sample.

The problem of a stroke which cannot be set to zero has been solved byDE2900373C3 by using a total of four further connecting rods or pushrods. Although this enables the stroke to be reset to zero, a specialgeometrical matching of the dimensions is necessary for the principleshown. The large number of joints and components used (and thus of themasses moved) means that the principle appears of little suitability fora cyclic application which is intended to be operated for many yearswithout play and wear.

The invention therefore has the object of providing a test device whichhas a simple construction, has low energy consumption, is subject to lowwear and in which a stroke amplitude between zero and a maximum valuecan be set and controlled during operation.

This object is achieved in accordance with the invention by means of atest device of the type mentioned at the outset in which the driveconnecting rods project from the ends of the rocker in the samedirection in the starting position of the test device.

In accordance with the invention, the crank mechanisms are arranged onopposite sides of the rocker. This arrangement means that therequirement for the connecting rods to project from the ends of therocker in the same direction is achieved in a simple manner.

The rocker is thus driven from both sides by means of connecting rods,which, in the starting position of the test device, are arranged equallyon the rocker, i.e. are at the same angle to the rocker. The test deviceaccording to the invention has the essential advantage that it hasexclusively pivot bearings and therefore slide blocks, which are subjectto very high wear, are not required. In addition, setting to zero strokeis possible. Finally, only a small number of components is needed,restricted to the rocker, the two connecting rods and the two crankmechanisms.

The test device according to the invention has very low energyconsumption compared with servo-hydraulic or servo-pneumatic testmachines, since hydraulic devices have high power losses in servovalves, causing the hydraulic medium to heat up, requiring furthersupply of energy for cooling thereof. In addition, hydraulic units mustbe designed for the maximum capacity of the load frame and of thehydraulic cylinders driven thereby, and consequently they do not workefficiently in the case of moderate and small test loads or testdisplacements. The generation of compressed air for servo-pneumaticsystems is likewise inefficient, predominantly owing to the generationof heat in the compressor.

The parts used for the test device according to the invention aremanufactured in large number for standard applications and have a simpledesign. Furthermore, the choice of the test parameters, such as thefrequency, load and distance, is absolutely flexible and not tied toresonance frequencies, as is often the case in other test machinedesigns. Since all components are connected to one another viaflexurally soft bearings or pivot bearings, a forcible control is given.The dynamics (acceleration, force/distance) during cyclic testing canthus be set to higher values than is possible in the case of machineshaving a magnetic linear drive.

Owing to the system-inherent inertness and design conversion of therotational movement into a stroke movement, very simple control or veryhigh control quality of the input variables, such as, for example,force, elongation or displacement, is possible, including the case ofsamples which exhibit a highly non-linear force/displacement behavior.

In order to reduce the load on the joints of the individual componentsor in order to be able to increase the test frequency, the crankmechanism is designed with an adjustable cam, in particular with a twincam. In order to be able to achieve very small amplitudes, the throw canoptionally be set to such a small amplitude, or where required, up totwice the throw of this small amplitude, by adjusting the cam, in whichcase the fine adjustment is carried out by mutual angular adjustment ofthe crank mechanisms. The static adjustment by means of a twin cam iscarried out, for example, by mutually adjusting two cams lying oneinside the other, also enabling a zero stroke to be produced.

Since component testing is often carried out not only with an amplitudearound the zero line, but additionally a prestress by means of which thecomponent is then loaded with an amplitude, the drive is attached to acarriage and can be prestressed with tension or pressure in the slidingdirection towards the second clamping device. This enables a base loadto be applied in the form of a base tension or a pressure, by means ofwhich the sample is then dynamically loaded (medium load withsuperimposed cyclic load). The forces here can be distributed in such away that they are exclusively in the pressure region or in the tensionregion or tension and pressure forces are applied alternately.

Tensile experiments and fatigue tests can be carried out with the testdevice according to the invention in static and dynamic types ofoperation. Furthermore, the test device and the actuators can be set upand arranged flexibly, enabling arrangement in a load frame or mountingon a mounting plate.

It is furthermore possible to synchronize a plurality of devices throughelectronic synchronization of the drive motors with one another. Thisserves for multiaxial load application to samples.

In accordance with the invention, the carriage can be movedmechanically, for example by means of a threaded spindle or toothedrack, or hydraulically. For precise setting of this prestressing force,provision is made, for example, for a load cell, which is connected, inparticular, to the sample.

A variant of the invention proposes that the workpiece is a sample or ahydraulic cylinder. By means of the hydraulic cylinder, the hydraulicmedium can be applied, for example, to an external sample, which isloaded, for example, under varying internal pressure.

It is also possible for components to be tested with a external pressureby using a hydraulic cylinder to convert the mechanical drive into ahydraulic pressure, which is more energy-efficient than generation ofpressure by means of a hydraulic unit and regulation by servo valve.

On the other hand, the hydraulic medium can be passed on to a second,external hydraulic cylinder, by means of which a poorly accessible orlarge component is loaded. By connecting a plurality of test devicestogether with hydraulic cylinders connected thereto in each case fortransmission of force to a sample, forces can be applied in variousdirections in order, for example, also to test multiaxial load states.

Further areas of application for the device according to the inventionare, inter alia, stamping machines, presses, pumps, vibrating screens,test machines for vibration testing or other oscillating equipment inwhich a means of adjusting the stroke amplitude during operation isnecessary or advantageous.

Further advantages, features and details of the invention arise from thesub-claims and the following description, in which particularlypreferred illustrative embodiments are described in detail withreference to the drawing. The features depicted in the drawing andmentioned in the description and in the claims may each be essential tothe invention individually or in any desired combination.

In the drawings:

FIG. 1 shows a first variant of the test device according to theinvention;

FIG. 2 shows a second variant of the test device according to theinvention;

FIG. 3 shows a depiction of the principle of the drive at zero stroke;

FIG. 4 shows a depiction of the principle of the drive with mediumstroke;

FIG. 5 shows a depiction of the principle of the drive at maximumstroke;

FIG. 6 shows various depictions of a twin cam;

FIG. 7 shows a sketch of the principle of the drive; and

FIG. 8 shows a further variant of the test device according to theinvention.

FIG. 1 depicts a first variant of a test device which is denoted in itsentirety by 10, in which a first actuator 14 for a quasi-static strokemovement, i.e. for a mean-load setting, is provided in a machine stand12. This first actuator 14 is connected via a rigid connection 16 to aforce transducer 18, which ends in a first clamping device 20. Thisfirst clamping device 20 is located opposite a second clamping device22, which is driven by a second actuator 24 for a cyclic (dynamic)stroke movement. A workpiece 26, in particular a sample 28, is clampedbetween the two clamping devices 20 and 22. The position of the actuator24 is adjustable and fixable along the load frame 30, depending on thesample size.

In the variant of the invention according to FIG. 2, the forcetransducer 18 is connected directly to the machine stand 12, where thesecond actuator 24 is arranged movably, by means of the first actuator14, along the load frame 30 of the machine stand 12, causing aprestressing force or a pressure to be applied to the workpiece 26.

FIG. 3 depicts the drive 32, provided in the second actuator 24, in itsstarting position, i.e. at zero stroke. This drive 32 has a rocker 34,in the center point 36 of which the second clamping device 22 is mountedvia a flexurally soft bearing (for example by means of an elastic stripof metal) or by means of a pivot bearing. A connecting rod 42 and 44 isrotatably mounted at each of the free ends 38 and 40 of the rocker 34.The connecting rods 42 and 44 are themselves each rotatably attached toa crank mechanism 46 and 48. These crank mechanisms 46 and 48 canrotate, for example, in the direction of the arrows 50, but rotation inthe opposite direction to the arrows 50 is also possible. In addition,rotation of the two crank mechanisms 46 and 48 in opposite directions ispossible.

In this position of the crank mechanisms 46 and 48, which are arrangedon opposite sides of the rocker 34 or point-symmetrically about thecenter point 36 of the rocker 34, the second clamping device 22 remainsat rest (zero stroke) when the crank mechanisms 46 and 48 rotate. Itshould also be noted that the crank mechanisms 46 and 48 rotatesimultaneously and generally at the same speed. The connecting rods 42and 44 project from the rocker 34 in the same direction, meaning thatthe angles 52 and 54 are of equal size.

FIG. 4 likewise shows the drive 32, but with the crank mechanism 48rotated by 90° (angle 56) in the clockwise direction (mathematicallynegative). If the two crank mechanisms 46 and 48 are rotatedsimultaneously in this position, the second clamping device 22 completesan oscillating stroke movement 58, which is, for example, 28 mm.

In FIG. 5, the crank mechanism 48 is rotated by 180° in the clockwisedirection (angle 60) relative to the position shown in FIG. 3. If thetwo crank mechanisms 46 and 48 are now rotated (arrows 50), the secondclamping device 22 again completes a stroke movement 58, but this nowcorresponds to a maximum stroke movement of, for example, 40 mm. It isclearly evident from FIGS. 3 to 5 that the angular adjustment of thecrank mechanism 48 relative to the crank mechanism 46 enables a changein length of the stroke movement 58 to be set. In a refinement of theinvention, the crank mechanism 46 may additionally also be adjusted.

Simple adjustment of the throw of the crank mechanism 46 or 48 can beachieved, for example, by forming the crank mechanism 46 or 48 out of atwin cam 62. FIG. 6 shows a twin cam 62 of this type in perspective viewand in three cam positions. The stroke adjustment is achieved by asecond cam disk 112 being accommodated in an eccentric hole of a firstcam disk 110, with the journal 64 again being accommodated eccentricallyin the second cam disk 112.

The cam position depicted on the left shows the maximum stroke, at whichthe journal 64 adopts its maximum separation from the center of the twincam 62. In the cam position depicted on the right, the journal 64 islocated precisely in the center of the twin cam. This is achievedthrough the first cam disk 110 being rotated through 180° and the secondcam disk 112 retaining its alignment. The center depiction shows anintermediate position, in which the first cam disk 110 is rotatedthrough 90° in an anticlockwise direction. The individual positions ofthe cam disks 110 and 112 and of the journal 64 can be clamped, forexample, hydraulically or mechanically.

In FIG. 7, 80 denotes an actuator for angular adjustment of the crankmechanism 46 and 48, and 24 denotes the second actuator for producing anoscillating stroke. Also depicted is a drive motor 66, for example asynchronous motor or a servo motor, which drives the second crankmechanism 48 directly or indirectly via a transmission. The first crankmechanism 46 is driven via a drive means 68, for example a toothed belt70, which runs around the second crank mechanism 48 and four guidepulleys 72 to 78. The reference symbol 80 denotes an adjustment device,for example a spindle drive 82, by means of which a carriage 84 isadjusted in the direction of the arrow 86. By means of the adjustmentdevice 80, the position of the guide rolls 74 and 76 relative to thecrank mechanisms 46 and 48 is changed. Due to this change, the relativeangle position of the crank mechanisms to one another is adjustedthrough the drawn length of the drive means between the two crankmechanisms 46 and 48 being shortened or lengthened. Since the two guidepulleys 74 and 76 are adjusted simultaneously when the carriage 84 isdisplaced, the drive means' length in the arrangement shown does notchange in the case of an adjustment, and there is no need to regulatethe tension of the drive means 68 owing to changed positions of theguide rolls 74 and 76.

FIG. 8 depicts a third variant of the test device according to theinvention, in which the workpiece 26 is in the form of a hydrauliccylinder 88. The pressure chambers 90 and 92 of the hydraulic cylinder88 are connected to pressure chambers 94 and 96 of a second hydrauliccylinder 98 by means of hydraulic lines 100 and 102. The secondhydraulic cylinder 98 acts on a sample 28 and transfers the strokemovements produced in the first hydraulic cylinder 88. This enables, forexample, poorly accessible or very large samples 28 to be tested.Furthermore, a pressure accumulator 104 and a tank 106 are evident inFIG. 8. The connections to the pressure accumulator and to the tank 6can be blocked by means of magnetic valves 108.

1. Test device (10) for the static and dynamic testing of workpieces(26), having a first clamping device (20) and a second clamping device(22) for the workpiece (26), and a drive (32) for moving the secondclamping device (22), where the drive (32) has a rocker (34) on whichthe second clamping device (22) is mounted in a rotatable manner, andthe two ends of the rocker (34) are each connected to a rotatablymounted connecting rod (42, 44), and the free ends of the connectingrods (42, 44) are each coupled to a crank mechanism (46, 48),characterized in that the crank mechanisms (46, 48) are arranged onopposite sides of the rocker (34) and in that the connecting rods (42,44) project from the ends of the rocker (34) in the same direction inthe starting position of the drive (32), i.e. when the clamping device(22) has the amplitude zero, when viewed from the center point of therocker (34) in the direction of the ends thereof.
 2. Test deviceaccording to claim 1, characterized in that the second clamping device(22) is rotatably mounted at the center point (36) of the rocker (34).3. Test device according to one of the preceding claims, characterizedin that the second clamping device (22) is connected to the rocker (34)at the center point (36) thereof by means of a flexurally soft bearing.4. Test device according to one of the preceding claims, characterizedin that the two connecting rods (42, 44) are connected to the ends ofthe rocker (34) by means of a flexurally soft bearing.
 5. Test deviceaccording to one of the preceding claims, characterized in that thecrank mechanisms (46, 48) each have an adjustable cam.
 6. Test deviceaccording to one of the preceding claims, characterized in that thecrank mechanism (46, 48) is in the form of a twin cam (62).
 7. Testdevice according to one of the preceding claims, characterized in thatthe crank mechanisms (46, 48) rotate in the same or opposite directions.8. Test device according to one of the preceding claims, characterizedin that the crank mechanisms (46, 48) can each be driven at the samespeed by their own electric motor, where the desired relative angularposition of the two crank mechanisms can be adjusted by precise phaseregulation of the electric motors.
 9. Test device according to one ofthe preceding claims, characterized in that the crank mechanisms (46,48) can each be driven at different speeds by their own electric motor,where successive strokes differ in amplitude.
 10. Test device accordingto one of the preceding claims, characterized in that the crankmechanisms (46, 48) are connected to one another by a drive means (68,70), where the length of the section of the drive means (68, 70) undertension between the two crank mechanisms (46, 48) can be adjusted by achange in the position of guide rolls (74, 76), which in turn has theconsequence of a change in the angular position of the crank mechanisms(46, 48) with respect to one another.
 11. Test device according to claim10, characterized in that the guide rolls (74, 76) are coupled via acarriage (84), which can be moved mechanically, for example by means ofa threaded spindle (82), hydraulically or pneumatically and the positionof the guide rolls (74, 76) thus changed.
 12. Test device according toone of the preceding claims, characterized in that the first clampingdevice (20) is additionally connected to a quasi-statically actingactuator (14), which is suitable for achieving displacement of theworkpiece (26) relative to a second actuator (24) and thus producing aprestress of the workpiece (26).
 13. Test device according to one of thepreceding claims, characterized in that the cyclic drive (32) isintegrated into a dynamic actuator unit (24), and a quasi-staticallyacting actuator (14) is rigidly connected to the dynamic actuator unit(24), so that the static actuator (14) changes the position of thedynamic actuator unit (24) so as to produce a prestress of the workpiece(26), on which the cyclic strokes of the dynamic actuator unit (24) aresuperimposed.
 14. Use of a test device according to one of the precedingclaims, characterized in that a sample (28) or a hydraulic cylinder (88)is clamped in for the workpiece (26).
 15. Use of a test device accordingto claim 14, characterized in that the hydraulic cylinder (88)hydraulically drives an externally arranged second hydraulic cylinder(98).
 16. Use of a test device according to one of the preceding claims,characterized in that a plurality of test devices (10) aresimultaneously used synchronously or intentionally asynchronously andact on a workpiece (26) or a sample (28) through electronicsynchronization of the drives (32).